1. Field of the Invention
The present invention relates generally to optical devices and, more specifically, the present invention relates to optical add/drop devices.
2. Background Information
The need for fast and efficient optical-based technologies is increasing as the growth rate of Internet data traffic overtakes that of voice traffic, pushing the need for fiber optic communications. Transmission of multiple optical channels over the same fiber in the dense wavelength-division multiplexing (DWDM) system provides a simple way to use the unprecedented capacity (signal bandwidth) offered by fiber optics. Commonly used optical components in the system include WDM transmitters and receivers, optical add/drop multiplexers, and optical filters such as diffraction gratings, thin-film filters, fiber Bragg gratings, and arrayed-waveguide gratings.
Optical add/drop multiplexers are used in optical telecommunications and networking industries to add new channels and drop existing channels from multi-channel optical signals. Some known add/drop devices employ complex arrangements of optical demultiplexers and multiplexers or arrayed waveguide gratings (AWGs) in combination with 2×2 optical switches for each channel of the optical signal. Other commonly known optical add/dropmultiplexers employ fiber-based Bragg gratings and circulators. Integrating the circulators with the fiber Bragg gratings is a challenge for this approach.
A fiber Bragg grating is an optical fiber device that is constructed by creating periodic changes in the refractive index of fiber core materials along the fiber length. These index changes may be formed by exposing the photosensitive core to an intense optical interference pattern. With the changes in the refractive index along the fiber length, optical beams at a particular wavelength are reflected by the fiber Bragg grating while other wavelengths are allowed to propagate through.
A limitation with current fiber Bragg gratings is that the particular wavelength reflected by the fiber Bragg grating is substantially fixed. Consequently, if different wavelengths of light are to be reflected, different fiber Bragg gratings are utilized. In some fiber Bragg gratings, nominal adjustments to the reflected wavelength are made by physically stretching the fiber Bragg grating to modify its period. The disadvantages of this technique are that the tuning range to the reflected wavelength is relatively small and the optical fiber may suffer damage from stress and strain induced by the physical stretching.